Scrubbing apparatus and method

ABSTRACT

A method and apparatus for scrubbing gases with liquid. It employs at least one nozzle which discharges a stream of gas downwardly against the surface of a body of scrubbing liquid (e.g., water). The nozzle is made with converging flat side walls to provide an elongated discharge opening which extends horizontally over the body of scrubbing liquid. The impingement of the discharging gas upon the liquid body serves to depress the surface of the liquid to form a trough-like region. Some scrubbing action is caused by such impingement, and the impingement causes some of the liquid to be entrained in the gas flow whereby a gas-liquid mixture flows in opposite lateral directions from the sides of the trough-like region. The nozzle is provided with shield means whereby the movement of gas and entrained liquid from the trough-like region is confined. Preferably the method and apparatus makes use of a plurality of such nozzles disposed side by side.

United States Patent [191 are Aug. 6, 1974 SCRUBBING APPARATUS AND METHOD [5 ABSTRACT [76] Inventor: Ernest Mare, c/o Mr D. D. Melin, A method and apparatus for scrubbing gases with liq- Krebs Engineers, 1205 Chrysler Dr., uid. It employs at least one nozzle which discharges a Menlo Park, Calif. 94025 stream of gas downwardly against the surface of a body of scrubbing liquid (e.g., water). The nozzle is [22] Filed May 1973 made with converging flat side walls to provide an [21] Appl. No.: 357,673 elongated discharge opening which extends horizontally over the body of scrubbing liquid. The impingement of the discharging gas upon the liquid body 5543353933; Serves to depress the Surface of the liquid to form a E 58] d I84 95 244 trough-like region. Some scrubbing action is caused by 0 care such impingement, and the impingement causes some of the liquid to be entrained in the gas flow whereby a [56] References cued gas-liquid mixture flows in opposite lateral directions UNITED STATES PATENTS from the sides of the trough-like region. The nozzle is 2,004,467 6/1935 Hawley 55/95 X provided with shield means whereby the movement of 2.06l.3 4 1/ Bingman l t 261/119 R gas and entrained liquid from the trough-like region is Selway X confined Preferably the method and apparatus makes 2 use of a plurality of such nozzles disposed side by side.

Primary Examiner--Samih N. Zaharna Assistant Examiner-Richard W. Burks Attorney, Agent, or F irm-Flehr, Hohbach Test, V Albritton & Herbert 5 Claims, 5 Drawing Figures PAIENTEDMIB 14 I 3.827. 216

SHEET 2 U? 2 SCRUBBING APPARATUS AND METHOD BACKGROUND OF THE INVENTION This invention relates generally to methods and apparatus for the scrubbing of gas with a liquid scrubbing medium, for the purpose of removing foreign material.

One effective type of scrubbing apparatus is disclosed in South African Pat. No. 66/7061, entitled Improved Means for Carrying Out Gas Scrubbing Operations, in which a nozzle having a circular discharge opening is disposed in the upper part of a reservoir that is adapted to contain a body of scrubbing liquid underlying the nozzle. The nozzle is provided with an annular shield near the lower end of the same and spaced above the liquid surface. The gas to be scrubbed is discharged downwardly through the nozzle and caused to impinge upon the surface of the liquid. This causes a bowlshaped depression in the surface of the liquid, and the gas with entrained liquid is caused to discharge in radial directions from the region of depression and through the space underlying the annular shield. In some instances an impingement screen is provided which depends from the annular periphery of the shield. Suitable means such as an overflow wier is provided for maintaining the level of the liquid body substantially constant.

In copending US. application Ser. No. 221,638, filed Jan. 28, 1972, there is disclosed an improvement to the above described scrubbing method and apparatus, wherein a plurality of nozzles having annular discharge orifices are used. This improved apparatus is capable of being built to attain greater scrubbing capacity and efficiency.

While the methods and apparatus disclosed in said South African Patent and said application are effective for the purposes desired, it has been found that they possess certain inherent energy losses due to friction between the high velocity gas flow and the surfaces of the nozzles. Also the scrubbing efficiency is not as high as is desired, which is attributed to the circular discharge openings which form bowl-shaped depressions. Such circular openings have a width determined by the cross-sectional flow area and this imposes a limitation on the ratio between the volume of gas flow and the effective liquid surface area of the depression. In addition, the cost of producing a high capacity unit making use of a plurality of nozzles as disclosed in said copending Application Ser. No. 221,638 is relatively high compared to that of the present invention when made to have the same operating capacity.

SUMMARY OF THE INVENTION In general, it is an object of the present invention to provide a gas scrubbing method and apparatus of the prior type referred to above, but which is characterized by relatively low energy loss due to friction between the high velocity gas stream and the surfaces of the nozzles.

Another object is to obtain more effective impingement of the gas with the surface of the scrubbing liquid, thus promoting separating efficiency.

Another object is to make possible the manufacture of such gas scrubbers in relatively high capacity units, and to have the same characterized by low energy loss and high separating efficiency.

Another object of the invention is to provide apparatus which is simpler and more economical to manufacture than apparatus as shown in said South African Pat. and application Ser. No. 221,638.

In general, the present method and apparatus makes use of a reservoir adapted to contain a body of scrubbing liquid. At least one gas nozzle is disposed within the reservoir above the liquid surface, and this nozzle is arranged to discharge gas downwardly upon the surface of the liquid. The lower end of this nozzle provides a relatively narrow and elongated discharge opening, or in other words a discharge opening which is relatively long compared to its width. Gas discharging through this opening against the surface of the liquid serves to depress the surface in a troughlike region. The gas after impinging with the liquid body flows outwardly with entrained liquid in directions laterally from the sides of the trough-like region. The nozzle is provided with shield means serving to confine the space between the same and the surface of the liquid, thereby confining the outward flow of gas and entrained liquid. Preferably a plurality of such nozzles are employed with the nozzles being disposed side by side to produce adjacent and parallel trough-like depressed regions.

Additional objects and features of the invention will appear from the following description in which the preferred embodiment has been disclosed in detail in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view, partly in section, schematically illustrating scrubbing apparatus incorporating the invention.

FIG. 2 is a plan view of the apparatus shown in FIG. 1, with certain parts broken away.

FIG. 3 is an enlarged view looking toward one side of one of the nozzles.

FIG. 4 is a cross-sectional view taken along the line 4-4 of FIG. 3.

FIG. 5 is an enlarged detail showing means for introducing scrubbing liquid into a nozzle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates apparatus consistng of a reservoir or tank 10 adapted to contain a body 11 of water or other suitable scrubbing liquid. Suitable means are used to maintain the liquid at a constant level. This may consist of means for continuously introducing a small amount of liquid into the reservoir, together with a suitable overflow wier (not shown) that may be located on one side of the tank. As viewed in plan, the tank in this instance is rectangular shaped. The lower portions l2, l3 and 14 of the tank can be constructed to facilitate the settling out of solids. The walls forming these portions are convergent and the settled out solids may be removed from time to time through the connecting valve controlled pipes l6, l7 and 18.

Within the reservoir and above the liquid body there is at least one and preferably a plurality of nozzles 19. The upper ends of these nozzles communicate through the top wall 21 of the reservoir, with the manifold 22 which receives gas which is to be scrubbed.

A suitable construction for the nozzles is shown in FIGS. 3-5. The substantially flat side walls 23 are convergent downwardly and connected with end walls 24, which may likewise be downwardly convergent. This provides a substantially rectangular shaped discharge opening or orifice 26 at the lower end of the nozzle. The upper wall 27 of the nozzle, which is attached to the side and end walls 23 and 24, is provided with a rectangular opening to receive the coupling duct 28, which is likewise rectangular as viewed in plan. Assuming flow of gas at a substantial static pressure into the manifold 22, it will be evident that the flow through each nozzle increases in velocity, thus providing a high velocity discharge of gas from the discharge opening 26.

The shield means carried by the nozzle near its lower end is made in two portions 29. Each portion can be made of suitable sheet metal attached to the side wall 23 of the nozzle, with the outer margin bent upwardly as shown at 31.

In conjunction with each nozzle it is desirable (but not essential) to provide impingement means 32 which aids in the removal of material from the gas flow. Such impingement means may be in the form of a screen of metal rods depending from the outer edges of the shield portions 29. Walls 33 are attached to the end walls 24 of the nozzle, and depend downwardly to enclose the ends of the space that are generally surrounded by the impingement screen 32 and the shield portions 29.

It is desirable in practice to introduce some scrubbing liquid directly into the nozzles. Thus as shown in FIG. a pipe 34 may extend into the upper part of each nozzle, and beneath the discharge end of this pipe a distributing wier 36 can be provided to aid in distributing the introduced water over the length of the mozzle.

At one side of the tank the gas is removed from the upper portion through the duct 37 and eliminator 38 (FIG. 2). Location of the exhaust duct as shown in FIG. 2 makes for low exhaust velocity and thus facilitates removal of liquid by the eliminator.

The method and operation of the apparatus is as follows: The stream of gas to be treated, which may be stack or exhaust gases containing dust particles, is supplied to the manifold 22 at a substantially constant static pressure, as for example by connecting the manifold to the discharge side of a blower. Flow from the manifold 22 is distributed to the nozzles and flows downwardly through the nozzles 19 with increasing velocity. The gas discharging from the lower ends of the nozzles impinges against the liquid to form trough-like depressions. These trough-like depressions are indicated at 39 in FIG. 1. Such impingement causes a scrubbing action on the gas, with separation and entrapment of solid dust particles in the liquid. In addition, the gas flowing laterally and out from each depression 39 picks up and entrains liquid, whereby gas discharging laterally through the spaces 40 below the shield portions 29 is in fact gas with entrained liquid, or in other words, a gas-liquid mixture. The liquid existing in this flow may be in part relatively thin liquid films and in part droplets of varying size. Turbulence is also present in this gas flow and in the spaces 40, with the result that there is effective contact of gas with surfaces of entrained liquid, thus promoting wetting of solid particles and entrainment of solid particles with liquid. Although the velocity of the gas discharging from a nozzle is relatively high, the velocity decreases rapidly after initial impingement due to the expanding flow area. Turbulent gas flow together with entrained liquid is also present in the spaces 41 between the nozzles and the shields, and from these spaces the gas flows upwardly for discharge through the eliminator 38. Within the spaces 41 there is cross-intermingling of gas and liquid moving in opposite directions, thus providng a region of cross-turbulence which again promotes effective and efficient scrubbing action. It will be apparent from FIG. 2 that the region 41 within which this action occurs extends for the horizontal length of the nozzles, or in other words for the length of the shield portions 29 as viewed in plan.

The depending impingement screen 42, when used, functions to provide surfaces against which entrained liquid impacts, thus causing entrained liquid to be broken up into smaller droplets. In addition, the screen provides vena contractae and venturi throats which further bring into contact the gases to be scrubbed and the liquid.

The relatively high scrubbing efficiency attained is attributed largely to the use of relatively narrow gas streams issuing from the nozzles, in contrast with the size required for a circular discharge opening of the same flow capacity. The narrow elongated high velocity stream provides an effective liquid surface area in the depressed region which is substantially greater than a depressed bowl-shaped surface formed by a circular nozzle opening, for the same flow capacity. This makes for more effective contact between the gas and the liquid surface, and more effective scrubbing action. In addition, as previously mentioned, the nozzle construction herein described is relatively simple and inexpensive to manufacture.

Although the invention has been described as applicable to the separation of dust particles from gases, it is also applicable where it is desired to remove gaseous pollutants from industrial waste gases by scrubbing action with water or other liquid. In some instances both solid dust particles may be removed together with absorption of gases. Also the invention can be used where it is desired to effect aeration of a liquid medium, as for example the introduction of atmospheric air or oxygen into water. In addition it can be used to promote chemical reactions between liquids and gases. All of the foregoing is embraced in what is commonly known as a scrubbing action.

By way of example the nozzles can be constructed to provide discharge openings 26 that are about 2 inches wide and 4 feet long. The gas may discharge from these openings at velocities within a wide range of say 8,000 to 30,000 feet per minute, with effective removal of solid dust particles.

1 claim:

1. A method of scrubbing gas with a scrubbing liquid, the method making use of a liquid body together with means for directing and discharging gas to be scrubbed against the surface of the body and shielding means overlying the surface of the liquid, the method comprising directing the flow of gas downwardly toward the surface of the liquid body with increasing velocity to cause impingement upon the liquid surface over a horizontal area extending longitudinally for a distance many times its width, the flow velocity against the liquid being such as to cause the liquid surface to be depressed in a trough-like region with entrainment of scrubbing liquid from the body and with free flight of such entrained liquid laterally from the depressed trough-like region, and confining the vertical dimension of the spaces along the sides of such depressed trough-like region by said shield means whereby flow of gas with entrained liquid occurs in directions laterally from said trough-like region between the surface of the liquid and the corresponding shield means.

2. A method as in claim 1 in which the gas is separated into at least two of said streams in laterally spaced parallel relationship whereby at least two laterally spaced and parallel trough-like depressions are formed.

opening having a length many times its width, the lower end of said nozzle being disposed horizontally, manifold means for delivering flow of gas to said nozzle, and shield means mounted upon the nozzle adjacent the lower end of the same, portions of said shield means extending in a general horizontal direction from said converging side walls, discharge of gas from said nozzle being caused to impinge upon the surface of the liquid to depress the same in a longitudinally extending trough-like region immediately underlying the nozzle, said shield means serving to provide confined spaces between the same and the surface of the liquid on both sides of the nozzle whereby gas after impingement with the liquid body flows outwardly with entrained liquid through the confined spaces to promote scrubbing action between the gas and liquid.

5. Apparatus as in claim 4 in which a plurality of said nozzles are provided, said nozzles being disposed side by side whereby the discharge of gas from said devices serves to depress the liquid surface in parallel troughlike regions. 

2. A method as in claim 1 in which the gas is separated into at least two of said streams in laterally spaced parallel relationship whereby at least two laterally spaced and parallel trough-like depressions are formed.
 3. A method as in claim 2 in which the mixture of gas and liquid discharging from each of said trough-like regions is caused to co-mingle with turbulence, with the gas and entrained liquid discharging from at least one adjacent trough-like region.
 4. In gas scrubbing apparatus, a reservoir or tank adapted to contain a body of scrubbing liquid, at least one gas discharge nozzle disposed within the upper part of the reservoir, said nozzle having substantially flat converging side walls forming a discharge orifice or opening having a length many times its width, the lower end of said nozzle Being disposed horizontally, manifold means for delivering flow of gas to said nozzle, and shield means mounted upon the nozzle adjacent the lower end of the same, portions of said shield means extending in a general horizontal direction from said converging side walls, discharge of gas from said nozzle being caused to impinge upon the surface of the liquid to depress the same in a longitudinally extending trough-like region immediately underlying the nozzle, said shield means serving to provide confined spaces between the same and the surface of the liquid on both sides of the nozzle whereby gas after impingement with the liquid body flows outwardly with entrained liquid through the confined spaces to promote scrubbing action between the gas and liquid.
 5. Apparatus as in claim 4 in which a plurality of said nozzles are provided, said nozzles being disposed side by side whereby the discharge of gas from said devices serves to depress the liquid surface in parallel trough-like regions. 